The present invention relates to a liquid jetting apparatus having a capping device for sealing a nozzle forming face of a liquid jetting head.
An ink jet recording apparatus includes a recording head mounted on a carriage which is reciprocatively moved in a main scan direction, and a recording medium feeder for intermittently feeding a recording medium, such as a printing paper, every feeding quantity in a sub-scan direction. To record, the recording head ejects ink drops toward the recording medium while the recording head is moved in the main scan direction.
A mono color ink jet recording apparatus normally uses one recording head. A full color ink jet recording apparatus includes a black ink recording head for ejecting black ink, and a color recording head for ejecting color inks of yellow, cyan, magenta and the like.
A principle of causing the recording head to eject ink in the ink jet recording apparatus follows. As known, ink is pressurized at a predetermined pressure in a pressure generating chamber. On the basis of the pressure, the ink is ejected in the form of an ink drop of a controlled size toward the recording medium through each nozzle orifice in the nozzle forming face. Accordingly, an ink ejection characteristic of the ink ejection from the nozzle orifice of the recording head must be maintained invariable. If the ink ejection characteristic varies, the record quantity will be deteriorated.
The ink ejection characteristic of the recording head varies by hardening of ink in the nozzle forming face, nozzle clogging by dust attaching, air bubble entering through the nozzles and others. To cope with this, to fixedly maintain the ink ejection characteristic of the recording head, the ink jet recording apparatus includes an ejection characteristic maintaining device which eliminates factors to vary the ink ejection characteristic to thereby maintain the ink ejection characteristic of the recording head invariable.
Firstly, the ejection characteristic maintaining device usually is equipped with a capping device. In a non-recording mode, the capping device seals the nozzle forming face to isolate the nozzle orifices from exterior to thereby suppress drying of ink and hence increase of ink viscosity.
Even in a state that the nozzle forming face is sealed with the capping device, it is impossible to completely prevent the clogging of the nozzle orifices and the entering of air bubbles into the ink passages. Secondly, the ejection characteristic maintaining device is equipped with a suction device capable of causing the nozzle orifices to forcibly discharge ink therefrom by sucking in order to remove the clogging of the nozzle orifices and the air bubbles entered. The suction device applies a negative pressure to the nozzle orifices in a state that the nozzle forming face is sealed with the cap member, to thereby cause ink to be discharged, by sucking, from the nozzle orifices, whereby the clogging and air bubble entering are removed. The forcible ink sucking/discharging process carried out by the suction device is called a cleaning. Usually, the cleaning process is performed when the recording apparatus, which is not used for a long time, is operated again or when a user recognizes deterioration of a quality of a recorded picture, and operates a dedicated switch on an operation panel of the apparatus.
When the forcible ink sucking/discharging process is performed by the suction device, ink possibly scatters and attaches onto the nozzle forming face of the recording head, and the turbulence of meniscuses is caused in the nozzle orifices. Further, foreign materials tend to attach to the nozzle forming face of the recording head as time elapses. Thirdly, to cope with this, the ejection characteristic maintaining device is equipped with a wiping device for wiping the nozzle forming face as the necessity arises. The wiping device includes a wiping member formed of an elastic material of rubber, for example, and a base end of the wiping member is compressively supported with a holder. To clean the nozzle forming face, the wiping member is moved relatively to the nozzle forming face, while elastically pressing an edge of a tip part of the wiping member or its vicinal part against the nozzle forming face. The cleaning operation by the wiping member is called a “wiping operation”. The “wiping operation” wipes ink and dust from the nozzle forming face, and uniformly arranges the meniscuses in the nozzle orifices, in other words, it stabilizes the meniscuses.
As described above, the capping device has two functions, a function to maintain the ink ejection characteristic by sealing the nozzle forming face, and a suction assist function to increase a negative pressure and a suction efficiency when the cleaning operation for forcibly discharging ink from the recording head is performed by the suction device in a manner that the capping device comes in close contact with the nozzle forming face. In consideration of those two functions, the capping device needs to have an area large enough to seal the nozzle forming face of the recording head. For this reason, in design the capping device, emphasis is placed on the securing of a necessary area, but little consideration is given to a volume of the cap member for the reasons given below.
When the suction operation is performed by the suction device, the ink discharged from the recording head is pulled to the suction device being under a negative pressure. Accordingly, there is no idea of securing a predetermined volume of the cap member or larger. Far from it, it is considered that if a space is present within the cap member in a state that the recording head is sealed, the nozzles will be dried. And, to reduce the size and manufacturing cost of the apparatus, attention is given to how to reduce the volume of the cap member as small as possible.
Accordingly, the volume of the related cap member is determined independently of the volume of suction ink in the suction operation, and efforts are made to reduce its size. However, where the volume of the cap member is small, a space of the cap member is filled with waste ink during the suction operation, and the waste ink sometimes reaches the nozzle forming face. If the suction device is stopped in a state that the cap member is thus filled with ink, waste ink flows back to the nozzles since the head side is under a negative pressure. As a result, dust, viscosity increased ink, air bubbles and the like enter the nozzles, and further the composite ink enters there to possibly cause color mixture. Further, when much ink attaches to the nozzle forming face, much ink is transferred to the wiper in the wiping operation, possibly causing the ink to scatter around.
Also, a technique that an ink absorbing member is put in the related cap member is used. Attempt is made, by retaining ink in the ink absorbing member, to prevent the nozzles from being dried at the time of the sealing, to suppress the suction ink from bubbling in the suction operation, and to prevent generation of ink mist in the flushing operation. Even if the ink absorbing member is put in the cap member, when the cap member is filled with ink, ink comes in contact with the nozzle forming face, and the problems stated above arise.
To cope with this, a related technique executes a fine quantity suction, which slightly operates the suction device during the first cleaning operation, several times to thereby prevent the back flow of the waste ink and the entering of air bubbles. To effect such a fine quantity suction, a dedicated sequence must be incorporated into a control sequence. Further, the cleaning time is increased by a time taken for the fine quantity suction.